1. Technical Field
The present invention relates to an automatic original feeding device for use in an image reader such as an image scanner and an IIT (Image Input Terminal) and an image forming apparatus such as a copying machine, a FAX and a composite machine, and an image reader and an image forming apparatus using the automatic original feeding device, and more particularly, to an automatic original feeding device supported on the upper face of a platen glass of an image reader for reading an image of the original passing through the original reading position set along a straight line on the upper face of the platen glass disposed at the upper end and feeding the original to pass through an original reading position, and an image reader and an image forming apparatus using the automatic original feeding device.
2. Related Art
(Misregistration in Scan Direction)
The position of an original in the scan direction when the original fed by the automatic original feeding device passes through an original reading position is controlled to become a preset reference position in the scan direction. If the position of the original in the scan direction in passing through the original reading position is deviated from the preset reference position in the scan direction, the position of an original image read by the image reader in the scan direction is deviated. In this case, if the original image is formed on an image recording paper without correcting the position of the original image which is read with a misregistration in the scan direction, the position of a copied image for the original formed on the image recording paper is deviated from the scheduled position in the scan direction.
Accordingly, a technology for measuring the amount of deviation of the position of the original in the scan direction (amount of misregistration in the scan direction) in passing through the original reading position from the preset reference position in the scan direction is so far well known, in which the position of the image on the image recording paper in the scan direction is adjusted according to measurements of the amount of misregistration in the scan direction.
(Misregistration in Sub Scan Direction)
Also, the position of a read image of the original in the sub scan direction is defined depending on an image reading start time of the original passing through the original reading position and an original former edge passage time at which the former edge of the original passes through the original reading position. Accordingly, the position of the read image for the original in the sub scan direction is controlled by adjusting the original former edge passage time with respect to the image reading start time. If the position of the read image for the original in the sub scan direction is deviated from the preset reference position in the sub scan direction, the position of the original image formed on the image recording paper is deviated from the scheduled position in the sub scan direction, when the original image is formed on the image recording paper without correcting the position of the original image read with a misregistration in the sub scan direction.
Accordingly, a technology for measuring the amount of deviation of the position of the original in the sub scan direction (amount of misregistration in the sub scan direction) in passing through the original reading position from the preset reference position in the sub scan direction is so far well known, in which the position of the image on the image recording sheet in the sub scan direction is adjusted according to measurements of the amount of misregistration in the sub scan direction.
(Original Size Magnification (Scan Direction Magnification and Sub Scan Direction Magnification))
The originals of regular sizes such as B5, B4, A4 and A3 are employed in most cases. However, when the image at equal magnification of the original image is formed on the recording paper, the recording paper of regular size such as B5, B4, A4 or A3 is used. In this case, where the original of A4 size is used, the recording paper of A4 size is employed. Though the reference value of regular A4 size is set, the size of A4 original actually used may change due to a size error occurring by cutting it into the A4 size, or depending on the temperature and humidity, and may be different from the reference value in some cases. Accordingly, there is a size error between the original of A4 size and the recording paper of A4 size. For instance, when the size of the A4 original is larger than the reference value of regular A4 size, and the size of the A4 recording paper is smaller, the size of the original and the size of the recording paper may be considerably greatly different. In this case, the position and the size of the image formed on the recording paper will shift when the copy image of the original image is formed on the recording paper without adjusting the size and the position of the read original image.
Accordingly, a technology for measuring the magnification in the scan direction length and the sub scan direction length (scan direction magnification and sub scan direction magnification) of the original in passing through the original reading position with respect to the preset reference value is so far well known, in which the magnifications of the image on the image recording paper in the scan direction and the sub scan direction are adjusted according to measurements of the magnification.
(Skew)
In most cases, the original is stopped temporarily at an original registration roll disposed on the upstream side of the original reading position in the original feeding direction, to form a loop at the former edge of the original, and then is fed to the original reading position. In this case, the amount of original skew is generally small, where there is no problem. However, when the axis of the original registration roll is inclined in a direction vertical to the original feeding direction due to some cause, the amount of original skew may become large. When the skew is large, the original image is inclined on the recording paper, if the read original image is directly formed on the recording paper, because the read original image is inclined.
Accordingly, a technology for measuring the amount of skew to know whether or not there is a large skew in the read image is so far well known.
When the amount of skew in the original is large, the inclination of the axis of the original registration roll may be adjusted by the service engineer, or automatically adjusted by providing a function of automatically adjusting the axis of the original registration roll.
Moreover, a technology for adjusting the skew by adjusting the inclination of a side guide (sheet guide for guiding one side of the recording sheet in the width direction) on the upstream side of the registration roll without forming a loop with the registration roll in a feeding device for the image recording sheet, but not the original registration roll, is so far well known.
Even if the automatic original feeding device employs the side guide, when the skew is large in the original image, the skew may be adjusted by calling the service engineer, or automatically adjusted by providing a function of automatically adjusting the inclination of the side guide in the automatic original feeding device.
Accordingly, if the misregistration of the copied image on the recording paper in the scan direction or sub scan direction, the original size magnification or the skew occurs due to the misregistration of the original image read at the reading position, the misregistration of the copied image on the recording paper is caused. To correct this misregistration, a technology for measuring the misregistration, the original size magnification or the skew is so far well known.
A technology for detecting and correcting the misregistration based on a difference between the detection position of the read image and the reference position stored in the memory by running the original having a test chart has been known.
A technology for detecting and correcting the misregistrations of the original at the original reading position in the scan direction and the sub scan direction by running the black original and sensing the original edge based on the contrast between a member opposed to the original reader and the black original has been known.
In the related arts described above, it is required to prepare the special original usually not provided, that is, an original having the test chart or the black original. Therefore, there is a problem because the special original must be prepared in practice though there is a feasibility.